1. Field of the Invention
This invention pertains to apparatus for reducing friable materials into coarse and fine fractions, and more particularly to improvements in the arrangements and operation of such apparatus.
2. Description of the Prior Art
There are a number of friable materials which are rendered useful for commercial and/or industrial purposes after being reduced from the raw state in which the size or chunks vary in a non-uniform manner. Some such materials need to be dried or have the moisture considerably reduced, and that requires a heat source.
An early form of apparatus for drying or dehydrating material disclosed the intentional recombining of coarse and fine materials discharged from a hammer mill, and reference is made to Arnold et al U.S. Pat. No. 2,770,543 of Nov. 13, 1956. In the apparatus of Weston et al U.S. Pat. No. 2,916,215 of Dec. 8, 1959, all the material produced in a grinding mill is moved in a common stream to a classifier where the oversize coarse fraction is removed from the main product of a finer size.
It is known that extreme fines removed from friable material can be used as a source of fuel for generating drying heat for the rest of the material of desired size. Such apparatus is disclosed in Williams U.S. Pat. No. 3,794,251 of Feb. 26, 1974, as well as in Williams U.S. Pat. No. 3,826,208 of July 30, 1974. The separation of coarse and fine fractions produced in a reducing mill for friable materials is shown by Williams U.S. Pat. No. 4,061,274 of Dec. 6, 1977, however, the system requires all of the reduced material to be transported to a series of secondary components of equipment to effect the separation.
The problem with the apparatus of the known prior art is that the stripping of the fines from the coarse fraction must be effected outside the primary material reducing mill which calls for an excessive number of components. Furthermore, in many case, the reducing mill is incapable of allowing separation of the various fractions.